This invention relates generally to implants for repairing ducts and passageways in the body. More specifically, the invention relates to implant deployment apparatus.
Treatment or isolation of vascular aneurysms or of vessel walls which have been thickened or thinned by disease has traditionally been performed via surgical bypassing with vascular grafts. Shortcomings of this procedure include the morbidity and mortality associated with surgery, long recovery times after surgery, and the high incidence of repeat intervention needed due to limitations of the graft or of the procedure.
Vessels thickened by disease may be treated less invasively with stents which mechanically hold vessels open. In some instances, stents may be used subsequent to or as an adjunct to a balloon angioplasty procedure. Stents also have been described in conjunction with grafts where the graft is intended to provide a generally smooth interface with blood flowing through the vessel.
Generally, it is important that the stent or stent-graft be accurately deployed so that it may be positioned at the desired location. Endovascular stent or stent-graft deployment can be summarized as a two-step process. The first step is moving the stent within the vasculature to a desired location. The stent or stent-graft may be self-expanding or balloon expandable. In both cases, the implant is typically delivered in a collapsed state to facilitate delivery through relatively small vessel lumens. The second step involves some method of xe2x80x9clockingxe2x80x9d the stent or stent-graft into its final geometry so that it will remain implanted in the desired location.
A number of techniques for delivering self-expanding or balloon expandable stents and stent-grafts are known. In the case of a self-expanding stent or stent-graft, a restraining mechanism typically is used to keep the stent or stent-graft in its collapsed state during delivery. The restraining mechanism is later removed to allow the stent or stent-graft to expand and engage the vessel wall at the desired implantation site. In the case of a balloon expandable stent or stent-graft, a restraining mechanism typically keeps the expandable device in a collapsed position during delivery with an inflatable balloon positioned within the collapsed device. The restraining mechanism is later removed to allow for inflation of the balloon which causes the stent or stent-graft to expand so that it engages the vessel wall. Generally, tubular sheaths or tying elements, which may be in the form of a filament or thread, have been described to restrain the collapsed devices.
U.S. Pat. No. 4,878,906, to Lindemann et al., discloses balloon expandable stent-grafts which are deployed through a tubular sheath. The stent-grafts are forwarded in a collapsed state along the vessel until they are in the correct location where the sheath is withdrawn, allowing expansion of the balloon within the stent-graft. After the balloon has expanded the stent-graft into final position, the balloon is deflated and drawn back into the tubular sheath. An alternative deployment method disclosed by Lindemann et al., dispenses with the tubular sheath and uses a xe2x80x9cthreadxe2x80x9d wrapped around the stent-graft and balloon which can be withdrawn when balloon inflation is desired.
Pinchuk, U.S. Pat. No. 5,019,090, shows a helically wrapped spring stent which is deployed with a balloon expansion catheter through a xe2x80x9csheathxe2x80x9d which holds the stent and balloon catheter in a generally compressed state. Once the stent and balloon have been forwarded into the correct position along a lumen, the sheath is withdrawn. The balloon is then inflated, deflated, and withdrawn, leaving the stent in final implantation position.
U.S. Pat. No. 5,246,452, to Sinnott, discloses a porous vascular graft which is implanted with a tear-away removable nonporous sheath. Once the graft has been forwarded into the desired position, circulation is restored to the area and blood is allowed to clot inside of the porous graft. After five minutes of clotting, the nonporous sheath can be removed by cutting or by pulling a string which tears the sheath and pulls it away.
U.S. Pat. No. 5,344,426, to Lau et al., discloses an expandable stent which is preferably self locking when expanded. The stent is positioned over an expandable member such as a balloon catheter and covered by a one or two layer sheath which is connected to a guidewire. When the assembly of sheath, stent, and expandable member has been forwarded to the desired position, the sheath is removed by moving the guidewire distally. With the sheath pulled off of the stent, the expandable member can be activated to expand the stent into its final position.
U.S. Pat. No. 5,366,473, to Winston et al., discloses an assembly in which a vascular graft is held in a compressed state over a pair of stents by a sheath. The stents take the form of flexible sheets wound around a spool. After the spool has been inserted to the correct endovascular site, the sheath is withdrawn allowing the stents to unwind and press the graft against the vessel walls.
Strecker, U.S. Pat. No. 5,405,378, discloses an expandable prosthesis which is held in radially compressed condition by a releasable sheath. The sheath can be a strippable meshwork which allows the compressed prosthesis to expand when the meshwork is controllably unraveled.
Generally, the mechanisms described above involve a number of components that may increase operational complexity. In addition, the size and mechanical properties of these mechanisms may limit deliverability of implants in small vessels. Delivery accuracy also may be a problem as discussed.
The diameter of conventional telescoping stent sheaths may contribute to undesirable friction with the delivery catheter as the sheath is pulled from the stent and over a push rod during deployment. This may make deployment accuracy difficult to control. Push rods, which are used to push the stent through the delivery catheter and which typically have a length of up to about 100 cm, also may contribute to undesirable friction with the catheter. This problem may be exacerbated where the catheter bends along its path in the vasculature. The sheath may also reposition the stent as it is retracted.
The present invention generally involves a delivery apparatus for an implant, such as a stent or stent-graft. The delivery system generally comprises a sheet of material adapted to extend around at least a portion of a collapsed implant, such as a collapsed stent or stent-graft. The sheet of material may form a tubular member when extending around at least a portion of a collapsed member. The system also may include a coupling member for coupling portions of the sheet together to maintain the implant in its collapsed state during delivery to a desired site in a mammalian body. With this construction a smooth interface between the collapsed stent and a vessel lumen, as compared to thread-like restraining members, may be achieved.
According to another aspect of the invention, the sheet may be constructed of a thin material which does not significantly contribute to the structural rigidity or cross-sectional profile to the delivery assembly. This construction may also eliminate the need for external sheathing or a guide catheter and is believed to advantageously increase the ability of the surgeon to deliver the device to relatively remote sites and through small tortuous vasculature. In addition, the sheet may comprise implantable material so that after release it may remain with the stent at the desired site.
According to another embodiment of the invention, an assembly comprising a stent and a restraining member coupled to the stent is provided. The stent has a collapsed and an expanded state and the restraining member comprises a sheet of material adapted to be wrapped around at least a portion of the stent when the stent is in the collapsed state. Portions of the sheet are adapted for coupling to one another to maintain the sheet wrapped around at least a portion of the stent in its collapsed state. Thus, in one configuration, portions of the sheet are releasably coupled to one another so that the sheet maintains the stent in its collapsed state.
According to another aspect of the invention, the portions of the sheet that may be coupled to one another may be coupled with a filament or thread-like member. The stent may be expanded (or allowed to expand when a self-expanding stent is used) after the thread-like coupling member is removed such as by being remotely pulled by a pull line, which may be an extension of the coupling member. Since the pull line may also have a thread-like low profile, friction with the catheter, through which the pull line is pulled, and the pull line is minimized. It is believed that such construction may further facilitate deployment accuracy.
According to another aspect of the invention, multiple restraining members may be used. Alternatively, multiple coupling members may be used to couple multiple portions of one or more restraining members. These constructions can reduce deployment time and may reduce the time in which fluid flow may disturb the position of the implant as it is deployed.
According to another aspect of the invention, an assembly comprises a stent and a restraining member coupled to the stent. The stent has a collapsed and an expanded state and first and second portions that move relative to one another when said stent moves between its collapsed and expanded states. The said restraining member comprises a sheet of material adapted to be wrapped around at least a portion of the stent when it is in its collapsed state, and portions of the sheet being adapted for coupling to one another to maintain said sheet wrapped around at least a portion of the stent in its collapsed state. The said assembly further includes a member having a first portion coupled to the restraining member and a second portion coupled to one of the stent first and second portions.
According to another aspect of the invention, an expandable stent, which is restrained in a collapsed state with a restraining member, is released and the restraining member urged against the wall of the lumen in which the stent is placed. Since the restraining member remains at the site, the number of deployment steps can be reduced as compared to other techniques (e.g. pushing a self-expanding implant out the end of a radially constraining sheath and retracting the sheath).
According to another aspect of the invention, a method of preparing a stent for delivery comprises restraining a collapsed stent in a sheet of material which may be in the form of a tube and coupling side margins of the tube.
According to another aspect of the invention, an expandable stent (or stent-graft) is collapsed into a generally cylindrical or tubular restraining by pulling the stent through a tapered member and into a tubular restraining member.
The above is a brief description of some deficiencies in the prior art and advantages of the present invention. Other features, advantages, and embodiments of the invention will be apparent to those skilled in the art from the following description, accompanying drawings, and appended claims.